The invention discloses a nanometer zero-valent iron-loaded lignin-grafted bentonite composite material and a preparation method thereof, belonging to the technical field of functional materials. The composite material is characterized in that bentonite is grafted with lignin and is then loaded with nanometer zero-valent iron. Compared with the prior art, the composite material provided by the invention has the following advantages: nanometer zero-valent iron in the composite material has obviously improved dispersibility and stability, good wastewater treatment capability, and good promotion and application value.